The present invention relates to a process for examining a fuel assembly of a nuclear reactor and to an examining apparatus for performing this process.
It is known that during the operation of a nuclear reactor, particularly a water-cooled reactor, it is necessary to periodically check the fuel assemblies forming the reactor core. This check particularly serves to detect possible deformations of the fuel rods and/or the maintainance structure, the spacing of the rods and any possible risk of cracks. When the reactor is shut down, certain assemblies which have operated under pressure and high temperature are discharged and transferred with the aid of appropriate handling equipment to an examining machine used for checking them.
The prior art describes numerous designs of examining machines for nuclear reactor fuel assemblies.
For example, French Pat. No. 2 298 859, filed on Jan. 22, 1975 and entitled "Apparatus and Installation for Examining the Fuel Rods of a Nuclear Reactor" describes a machine of this type. It comprises examining means making it possible to collect information on the assembly to be examined, means for displacing the examining means with respect to the assembly to be examined and finally means for processing the information collected by the examining means.
The examining means are constituted by a prismatic endoscope, the means for displacing the endoscope being constituted by three moving carriages, the first moving vertically on slides parallel to the fuel rods of the assembly, the second moving horizontally on slides carried by the first carriage and the third moving horizontally perpendicular to the aforementioned carriage. Thus, the endoscope carried by the third carriage can be displaced in three perpendicular directions.
However, a disadvantage of a machine of this type is that the fuel assembly to be examined is held between two ends supports, which rigidly maintain it. These end supports exert stresses on the assembly. However, it is known that the frame of a fuel assembly is of a lightweight construction and easily deforms. Visual observation of the assembly and its metrology are therefore carried out after it has been deformed, so that the measurements are falsified.
According to another design, the measurement and examination of the assembly can be carried out when the latter is suspended by its upper end member. In this case once again the position of the assembly differs from the reference position used in metrology, because it is exposed to tensile stresses. However, the frame formed by the guide tubes is of a lightweight nature and is therefore liable to deform. Thus, the measurements will also be falsified if they are performed when the assembly is extended.